A retractor is an instrument used during surgery for drawing back and holding in position the edges of a surgical site. The opening created at the surgical site is maintained in a certain manner to provide at least surgical access and in some cases may be used to provide visual access as well. In use, retractors often put pressure on blood vessels. In some applications of retractors, such as, for example, surgery on the lower back, the retractor applies pressure to major blood vessels that supply blood to the pelvis and legs.
The human spine is composed of a column of thirty-three bones, called vertebrae, and the joining structures. The twenty-four vertebrae nearest the head are separate bones and are capable of individual movement. These vertebrae are generally connected by anterior and posterior longitudinal ligaments and by discs of fibrocartilage, called intervertebral discs, positioned between opposing faces of adjacent vertebral bodies. The remaining nine vertebrae are fused to form the sacrum and the coccyx and are incapable of individual movement. The vertebral body and the dorsal vertebrae enclose an opening termed the vertebral foramen, through which the spinal cord, a column of nerve tissue which communicates nerve impulses between the brain and the rest of the body, and spinal nerve roots pass and are protected from damage.
The intervertebral discs are sometimes damaged by local pressure on the spinal cord or excessive bending of the spinal cord which can result in disorders associated with blockage of the nerve impulses traveling along the spinal cord, in turn producing pain, paresthesia, or loss of motor control which must be resolved by removing the causative condition. Also, herniation of the intervertebral disc can occur, in which a small amount of tissue protrudes from the sides of the disc into the foramen to compress the spinal cord. Another common condition involves the development of small bone spurs, called osteophites along the posterior surface of the vertebral body, again impinging on the spinal cord.
Surgery is often required to correct the above and other problems. In one procedure, the involved vertebral bodies are exposed and the intervertebral disc is removed or replaced. When such a surgery is performed toward the lower portion of the spine major, blood vessels that supply blood to the legs and pelvis often need to be held out of the surgical site with retractors in order to perform the surgery. Excessive retraction of those major blood vessels can result in compromised blood flow to the pelvis and legs. Currently, direct palpation of pulse distal to the retractor is the only indication of excessive retraction.